Self-brazing cathode



R. S. BRIGGS SELF-BRAZING CATHODE July 27, 195.4

3 Sheets-Sheet l Filed Oct. 10. 1952 M WWW July 27, 1954 R. s. BRlcsGsSELF-BRAZING CATHODE Filed oct. 1o, 1952 3 Sheets-Sheet 2 IN1/grax.

July 27 1954 R. s. BRIGGs 2,684,886

SELF-BRAZING CATHODE Filed Oct. l0, 1952 l 3 Sheets-SheBt 3 F/@CBlCLEANINC OP METAL PARTS l OECREASE ANO IIYOROCEN BAKE NICKEL STRIKE IASSEMBLE CATHOOE COMPONENTS l MOUNT ON CATHOOE TUBE wITI-I HEATER COILAPPLY SUSPENSION OF NICKEL POwOER ON ALL JOINTS VACUUM SEAL ANO EvACUATEI HEAT CATHOOE ASSEMBLY TO BRAzINC TEMPERATURE IN VACUUM CATI-IOOEASSEMBLY BRAzEO r JNVENTOIL Patented July 27, 1954 UNITED STTES iaTENTOFFICE SELF-BRAZING CATHODE Application October 10, 1952, Serial No.314,153

(Cl. S16- 19) 3 Claims.

This invention relates to the brazing of metals and more particularly toa novel method of brazing the cathode component parts for an ultra highor microwave frequency magnetron.

Ultra high or microwave frequency magnetrons commonly employ oxidecoated cathodes as an electron emitting source. The oxidecoated cathodeis commonly cantilever-supported and centered within a multivaned anodeblock. A circular sleeve, coated or impregnated with an electronemissive coating may be supported by a stem and indirectly heated by aheater element communicating with said stem.

In the process of assembling the cathode in accordance with conventionalbrazing methods, the problem of contamination of parts, as well assputtering of brazing flux on surrounding parts arises in many cases.

Accordingly, an object of present invention is to provide a novel methodof brazing the electron emissive member.

The invention will be more clearly understood from the followingdetailed description and reference to the accompanying drawings, inwhich Figure 1 is a longitudinal cross sectional view of an illustrativeembodiment of an assembled magnetron cathode, vacuum sealed.

Figure 2 is an enlarged detail view of the component parts of thecathode in Figure 1.

Figure 3 is a now diagram of the process of this invention.

Referring now to the drawing, reference numeral l indicates an assembledcathode of an ultra high or microwave frequency magnetron, vacuum sealedand in final stage of assembly. The electron emitter 2 consisting of acircular sleeve of a refractory metal, desirably tungsten, coated orimpregnated with an emitting material is supported by cathode tube 4.

In detail, as shown in Figure 2, the electron emitter or cathode 3 isretained within cap 5 which is supported on the shank of cathode tube 4.In the illustrative embodiment, I have found molybdenum to be desirablefor cap 5 and cathode tube 4.

Cap 5, in the illustrative embodiment is composed of an eyelet section 6and ring l, frictionfitted over the tapered shank of eyelet 6.

The method of this invention resides in the assembly of cathode 3 andretaining cap 5 on supporting member 4.

According to the teachings of the invention as shown in the flow diagramFigure 3, the eyelet 6 and ring 1 are thoroughly cleaned by degreasngsolvents and are then baked in an atmosphere of hydrogen in thewell-known manner of the electronic art. In the next operation theseparts are plated with a nickel strike. For the purposes of thisspecication. the term strike is defined as a thin layer ofelectroplating having a thickness of approximately one hundredthousandths to one ten thousandths of an inch (ANON-.0001); saidelectroplating being applied by immersion for a period of short durationin a bath having low cathode efficiency and a high current. Cathode 3 isthen positioned on eyelet section 6 followed by retaining ring l. Thissubassembly is then friction-fitted over the shank of cathode tube dsubstantially as shown in Figure 2.

A suspension of nickel powder or any compound of nickel, such as nickeloxide, which can be reduced to finely divided nickel, and a smallquantity of nitrocellulose lacquer suflicient to make a pasty mixture isprepared. Other suitable mixing agents may be employed with comparableresults. However, I have used nitrocellulose lacquer to provide goodadherence. This mixture is next applied to the joints in the cathodesub-assembly indicated by reference numerals 8l`l.

The cathode sub-assembly is next provided with a heater element itsupported by legs I9 and Eil and housed within the cathode tube, Anelectrode 2l axially spaced and supported by dielectric spacers 22 and23 is electrically connected to leg 2li of the heater element.

The assembled cathode may then be provided with a glass envelope 24 andbe exhausted by conventional methods.

lectrode 2l is connected to a voltage supply suicient to heat thecathode to approximately 1300 C.-1400 C. Maintaining the cathode at thistemperature for approximately two minutes will result in the brazing ofthe joints of the cathode components to which the nickel powdersuspension has been applied.

The brazed cathode assembly will now be ready for further processing inthe manufacture of a complete tube.

The self-brazed cathode will be free from contamination, since brazingtakes place in an evacuated atmosphere. Further, this method of brazingfacilitates assembly of small parts which would present a seriousproblem under conventional brazing methods.

What I claim and desire to secure by Letters Patent is:

1. A method of assembling a self-brazing cathode comprisingT the stepsof degreasing and hydrogen baking a metallic retaining member composedof an eyelet section and ring section, depositing a thin layer of nickelplating thereon, assembling an electron emitter over said eyelet sectionfollowed by said ring section, mounting said assembled parts on acathode tube with a substantially hollow section provided with a heaterelement therein, applying a suspension of nickel powder and a mixingagent to the joints of the electron emitter, eyelet section, ringsection and the cathode tube at the point of Contact, providing anexternal connecting source for said heater element, vacuum sealing andevacuating the assembled components, and connecting a voltage source tothe heater element sufficient to heat the assembled evacuated and vacuumsealed component parts to a temperature surficient to cause the nickelpowder suspension to ilow and braze the assembled components.

2. A method according to claim l wherein said electron emitter iscomposed of a sleeve of a refractory metal and alloys thereofimpregnated with a thermionic material and said assembled evacuated andvacuum sealed component parts are heated to a temperature ofapproximately 1300 C. to 1400 C.

3. A method of assembling and brazing a cathode for an electron deviceof the magnetron type comprising the steps of plating a metallicretaining member including an eyelet and ring section with a thin layerof nickel, assembling a sleeve of a refractory metal coated with anemissive materialL over said eyelet section followed by said ringsection, mounting said as sembled parts on a tubular support memberhaving a hollow section with a heater coil therein, preparing asuspension of a nickel powder and a binding agent, applying saidsuspension to the point o contact of said sleeve, eyelet section, ringsection and the tubular support member, connecting an electrode to oneleg of said heater coil, sealing said assembled component parts in aVacuum retaining enclosure, exhausting the atmosphere within saidenclosure and connecting the end of said electrode to a voltage sourcenecessary to heat the assembled parts to a temperature of approximatelyl300 C. to 1400" C. in the reduced atmosphere.

Name Date Kelley Oct. 9, 1951 Number

1. A METHOD OF ASSEMBLING A SELF-BRAZING CATHODE COMPRISING THE STEPS OFDECREASING AND HYDROGEN BAKING A METALLIC RETAINING MEMBER COMPOSED OFAN EYELET SECTION AND RING SECTION, DEPOSITING A THIN LAYER OF NICKELPLATING THEREON, ASSEMBLING AN ELECTRON EMITTER OVER SAID EYELET SECTIONFOLLOWED BY SAID RING SECTION, MOUNTING SAID ASSEMBLED PARTS ON ACATHODE TUBE WITH A SUBSTANTIALLY PARTS ON A CATHODE TUBE WITH A HEATERELEMENT THEREIN, APPLYING A SUSPENSION OF NICKEL POWDER AND A MIXINGAGENT TO THE JOINTS OF THE ELECTRON EMITTER, EYELET SECTION, RINGSECTION AND THE CATHODE TUBE AT THE POINT OF CONTACT, PROVIDING ANEXTERNAL CONNECTING SOURCE FOR SAID HEATER ELEMENT, VACUUM SEALING ANDEVACUATING THE ASSEMBLER COMPONENTS, AND CONNECTING A VOLTAGE SOURCE TOTHE HEATER ELEMENT SUFFICIENT TO HEAT THE ASSEMBLED EVACUATED AND VACUUMSEALED COMPONENT PARTS TO A TEMPERATURE SUFFICIENT TO CAUSE THE NICKELPOWDER SUSPENSION TO FLOW AND BRAZE THE ASSEMBLED COMPONENTS.